Field of the Invention
This invention relates generally to a pattern recognition system and, more particularly, to a signal separation system to discriminate cytoplasms of white blood cells from a sample of whole blood in an automated classification of the white blood cells.
It is well known that an examination as to the classification of the white blood cells in whole blood and the existence of abnormal white blood cells therein is effectively used in the diagnosis of humans. The examination due to the classification of the white blood cells is therefore important in clinical examinations. In order to achieve an automatic examination for the classification of white blood cells, various techniques have been developed. There are, for example, techniques described in U.S. Pat. No. 3,827,804, "Color Separation for Discrimination in Pattern Recognition Systems" ; "The Classification of White Blood Cells", IEEE Transactions on Biomedical Engineering, Vol. BME-19, No.4, July 1972; and "Loukocyte Pattern Recognition", IEEE Transactions on Systems, Man and Cybernetics, Vol. CMC-2, No.4, July 1972. As described in the above publications, there is a system which recognizes white blood cells, especially the nuclei thereof, by discriminating a signal component of red blood cells from a sample of a whole blood by subtracting two signals from each other, each of which respectively corresponds to a green and a blue electric signal generated in response to respective green and blue light beams separated from a light beam which has passed through the sample of whole blood. This method utilizes the fact that the two signal components, as to the red blood cells included in the green and the blue light beams, are nearly equal to each other.
In order to classify the white blood cells automatically, however, it is necessary to determine the color of cytoplasm and the nucleus-cytoplasm ratio of the white blood cells, etc. It has been impossible to effect an automatic classification of white blood cells even from a detected image of the white blood cells due to the following. The sample of the whole blood is dyed with either one of a Wright Stain, A Giemza Stain, a Wright Glemza Stain and a May Giemza Stain. Due to the spectral absorbence of dyes in the sample of the whole blood the red blood cells appear reddish in the sample and the cytoplasm of the white blood cell appear light bluish and the nucleus of the white blood cell appear dark bluish. The absorption factor of the cytoplasms of the white blood cells, however, is generally lower than those of the nuclei thereof and of the red blood cells, and is nearly equal to that of the background in a bad part of the dye, and also depends upon the type of white blood cells even in a good part of the dye. Therefore, it is impossible to distinguish only the cytoplasms of the white blood cells with a fixed threshold level provided to discriminate the cytoplasms from others, so that information with respect to the cytoplasms thereof cannot be obtained by the above method.